The invention is directed to a method for determining the time of reclosing a circuit breaker.
The invention relates to a prior art as described in the report "Measures taken to reduce overvoltages when energizing no-load lines" by G. Koppl in Surges in High Voltage Networks, edited by K. Ragaller, Plenum Press New York 1980.
In electric systems which feed voltages of greater than or equal to 362 kV, the necessary insulation is determined by the circuit voltage loading. A critical situation arises during rapid reclosing of circuit breakers which were interrupted in response to earth shorts on a line. The problem is due to certain voltages which may develop on the line due to the prior interruption which voltage may interact adversely with the line voltage during reclosing of the circuit breaker. With a three-phase interruption due to a single-phase short, that is to say when all three poles of the circuit breaker are open, the last-quenching two poles of the unaffected phase interrupt an open line.
For the case of uncompensated lines containing capacitive voltage transformers, a load which changes only very slowly is left on the line. Therefore, during the rapid reclosing, switching does not take place when feed voltage and load are of opposite polarity. Thus, the polarities of the feed voltage and of the load remaining on the disconnected line are detected in the known method and reclosing takes place when the polarities are identical.
In shunt-compensated lines the precharged line capacity and the inductances of compensating chokes form a tuned circuit. Consequently, the voltage on the line side oscillates with a natural frequency which is determined by the degree of compensation and which is lower than the frequency of the feed voltage. It is therefore possible to close the circuit breaker when supply and line voltage have opposite polarities. In such case, unacceptably high switching overvoltages occur at the open end of the line.